Fuel cells that generate electric current by controllably combining elemental hydrogen and oxygen are well known. In one form of such a fuel cell, an anodic layer and a cathodic layer are separated by a permeable electrolyte formed of a ceramic solid oxide. Such a fuel cell is known in the art as a “solid-oxide fuel cell” (SOFC). Hydrogen, either pure or reformed from hydrocarbons, is flowed along the outer surface of the anode and diffuses into the anode. Oxygen, typically from air, is flowed along the outer surface of the cathode and diffuses into the cathode. Each O2 molecule is split and reduced to two O−2 ions catalytically by the cathode. The oxygen ions diffuse through the electrolyte and combine at the anode/electrolyte interface with four hydrogen ions to form two molecules of water. The anode and the cathode are connected externally through the load to complete the circuit whereby four electrons are transferred from the anode to the cathode. When hydrogen is derived from “reformed” hydrocarbons, the “reformate” gas includes CO which is also a fuel for the fuel cell and is converted to CO2 at the anode. Reformed gasoline is a commonly used fuel in automotive fuel cell applications.
Because a single cell is capable of generating a relatively small voltage and wattage, in practice it is usual to stack together, in electrical series, a plurality of such cells. Adjacent cells are connected electrically by interconnect elements in the “stack.” The outermost, or end, interconnects of the stack define electric terminals, or “current collectors,” which may be connected across a load.
A complete SOFC assembly typically includes auxiliary subsystems for, among other requirements, generating fuel by reforming hydrocarbons via a reformer; tempering via heat exchangers the reformate fuel and air entering the stack; providing air to the hydrocarbon reformer; providing air to the cathodes for reaction with hydrogen in the fuel cell stack; providing air for cooling the fuel cell stack; providing combustion air to an afterburner for unspent fuel exiting the stack; and providing cooling air to the afterburner and the stack. Such auxiliary subsystems may be mechanically integrated into an SOFC assembly or system by individual attachment to an Integrated Component Manifold (ICM) whereby all flows of gases are appropriately directed throughout the assembly.
In the prior art, a problem exists in providing a durable hermetic seal in the joint between each of the components and the ICM. In an SOFC being supplied with fuel from a reformer, for example, the fuel cell supply gas is provided directly from the reformer at an elevated temperature (800° C.-1000° C.). In the prior art, gasketing for gas seals at such temperatures requires special materials such as glass, silver foil, and/or mica. Such seals are difficult and expensive to fabricate and are prone to failure upon repeated thermal cycling, resulting in failure of the fuel cell assembly. Further, prior art mechanical seals typically exert relatively light compressive sealing loads, require high degree of flatness of the surfaces to be sealed, and tend to relax or lose resilience with time and use.
It is a principal object of the present invention to provide a permanently resilient and compliant gasket that maintains a high positive sealing pressure under all fuel cell use conditions, that is relatively easy to fabricate and install into a fuel cell assembly, and that can diffusion bond to the surfaces to be sealed.